藻礁為由殼狀珊瑚藻 (crustose coralline algae， CCA) 長期鈣化、堆積與膠結所形成之特殊沿岸礁體，具重要棲地功能與保育價值，且對懸浮沉積物與沉積壓力高度敏感。過去藻礁區水體環境評估多以懸浮沉積物濃度 (suspended sediment concentration， SSC) 為指標，對懸浮顆粒之組成、粒徑分布 (particle size distribution， PSD) 與絮凝狀態之了解仍相當有限。本研究以桃園觀新藻礁北永續利用區為場址，於 5 月 6 日至 6 月 11 日進行現地連續監測 (ADV、OBS、LISST、YSI EXO2) 並採集離散水樣，分析總懸浮固體 (TSS)、礦物／有機質組成 (FSS/VSS)、葉綠素 a (Chl-a) 及前處理後初級顆粒 (primary particles， PP) 粒徑，探討藻礁區懸浮顆粒之組成、粒徑分布，及其與水動力 (以示性波高 Hs 與平均水平流速 U 表示) 及有機質 (organic matter， OM) 之關係。 研究期間 Hs 約介於 0.2–0.8 m、U 約 0.02–0.33 m s⁻¹，離散水樣 TSS 約 12.7–132.2 mg L⁻¹，顯示懸浮濃度具高度變異。懸浮顆粒以礦物顆粒為主 (多數樣本高於 85%)，OM 比例約 2.4–23.2% 並具明顯時段變化。以現地 LISST 絮團粒徑與去 OM 後 PP 礦物粒徑之比值 (floc ratio) 量化絮凝程度，floc ratio 與 OM 呈顯著正相關 (r = +0.78，R² = 0.61)，高 OM 時絮團等效粒徑約為礦物骨架之 2.5 倍；絮團有效密度約 300–780 kg m⁻³，並隨 OM 增加而下降 (r = −0.52)。在控制水動力後，OM 仍為控制絮凝結構之主要組成因子；Chl-a 與 OM 關聯性降低，推測驅動絮凝之 OM 以非光合性有機碎屑或胞外聚合物為主，而非新鮮浮游植物。另一方面，水動力 (以 Hs 為代表) 與 TSS 高度正相關 (r = +0.88)，並使顆粒粒徑趨粗、粒徑分布趨窄、OM 比例下降及絮團破碎，反映再懸浮主導之物理過程。 綜合而言，藻礁區懸浮顆粒可大致區分為高水動力、礦物主導與低水動力、有機質主導兩種型態，其粒徑結構由水動力再懸浮與有機質絮凝之相對強弱共同決定。本研究以去 OM 粒徑對照之獨立方法，結果與生物凝聚作用 (bio-cohesion) 參與藻礁區懸浮顆粒絮凝之解釋一致，並顯示單以 SSC 不足以描述藻礁懸浮顆粒之環境效應，須一併考量其組成、粒徑分布、絮凝狀態與有效密度，可作為後續藻礁沉積壓力評估與保育管理之參考。;Algal reefs， formed by the long-term calcification， accumulation， and cementation of crustose coralline algae (CCA)， are ecologically valuable coastal reef systems that are highly sensitive to suspended sediment and sedimentation stress. Assessments of the water environment over algal reefs have largely relied on suspended sediment concentration (SSC)， whereas the composition， particle size distribution (PSD)， and flocculation state of suspended particles remain poorly understood. This study was conducted at the northern Sustainable-Use Zone of the Guanxin Algal Reef， Taoyuan， Taiwan. In-situ continuous monitoring (ADV， OBS， LISST， and YSI EXO2) and discrete water sampling were carried out from 6 May to 11 June to analyze total suspended solids (TSS)， mineral/organic composition (FSS/VSS)， chlorophyll-a (Chl-a)， and the particle size of pretreated primary particles (PP)， and to examine the composition and PSD of suspended particles in relation to hydrodynamic forcing (represented by significant wave height， Hs， and mean horizontal velocity， U) and organic matter (OM). During the study period， Hs ranged from about 0.2 to 0.8 m and U from about 0.02 to 0.33 m s⁻¹， while TSS in discrete samples ranged from about 12.7 to 132.2 mg L⁻¹， indicating high variability in suspended concentration. Suspended particles were dominated by mineral particles (>85% in most samples)， whereas OM accounted for approximately 2.4–23.2% with pronounced temporal variability. Flocculation was quantified using the floc ratio， defined as the ratio of the in-situ LISST median diameter to the OM-removed PP median diameter. The floc ratio was strongly and positively correlated with OM (r = +0.78， R² = 0.61); under high-OM conditions， the equivalent diameter of flocs was about 2.5 times that of their mineral skeleton. The effective density of flocs (≈300–780 kg m⁻³) decreased with increasing OM (r = −0.52). After controlling for hydrodynamic forcing， OM remained the primary compositional control on flocculation， and the decoupling between Chl-a and OM suggests that the OM driving flocculation is mainly non-photosynthetic detritus or extracellular polymeric substances rather than fresh phytoplankton. In contrast， hydrodynamic forcing (represented by Hs) was highly correlated with TSS (r = +0.88) and was associated with coarser and better-sorted particles， a lower OM fraction， and floc breakup， reflecting resuspension-dominated physical processes. Overall， suspended particles over the algal reef can be broadly divided into a high-energy， mineral-dominated type and a low-energy， OM-dominated type， and their size structure is jointly determined by the relative strength of wave-driven resuspension and OM-mediated flocculation. Using an independent OM-removal size-comparison approach， the results are consistent with a role of bio-cohesion in the flocculation of suspended particles over the algal reef， and demonstrate that SSC alone is insufficient to characterize the environmental effects of suspended particles， which also require consideration of composition， PSD， flocculation state， and effective density. These findings provide baseline information for future assessment of sedimentation stress and conservation management of algal reefs.
